<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>数值</title>
</head>
<body>
<!-- 整数, 浮点数, 大数-->
<script>
  //
  console.log(typeof 123, typeof 3.14, typeof 'abc',
  typeof false, typeof undefined, typeof null, // object
    // symbol               bigint
  typeof Symbol('key'), typeof 123n)

  function add(a, b) { return a + b }
  const apply = (a, b) => a + b
  // typeof 判断不了数组
  console.log(typeof [], typeof {}, typeof apply, typeof add,
  Array.isArray([]))

  let value = 10;
  value = 3.14;
  value = Infinity
  value = -Infinity
  value = NaN // 非数值, 和任何类型值都不同, 使用 isNaN 判断
  value = 999999999999999999999999999n
  console.log('value =>', value, typeof value)

</script>
</body>
</html>